I'm interested in the heirs of Peter the Great's co-Tsar and halfbrother Iwan V..

His daughter Anna Iwanova became Empress from 1730-1740. Her successor was her grand-nephew Iwan VI. He was the grandson of her sister Catherine who had been married to Karl Leopold Duke of Mecklenburg-Schwerin. Her sister had returned to Russia with her daughter Elisabeth Katharina Christine Herzogin zu Mecklenburg(-Schwerin) who converted to Russian Orthodox faith as Anna Leopoldowa.In 1739, during the reign of her aunt Anna Iwanowa the princess married Prince Anton Ulrich of Braunschweig-Wolfenbüttel. In 1740 her son Iwan was born and declared Tsar after Anna Iwanova's death. Anna Leopoldowa took on the title of Grand Duchess and regent of Russia for her son.

One year later, Elisabeth Petrowna, the daughter of Peter The Great deposed her son and her and sent her into exile. There she became mother of 4 more children: Catherine, Elisabeth, Peter and Alexej.

Anna Leopoldowa died 1746. Her husband stayed in captivity to be with their children till his death in 1776. In 1780 Catherine II. freed the four Braunschweig-siblings (their elder brother Iwan VI: had been murdered in 1764) and send them without any money into exile. They finally settled in Denmark. The last of the four, princess Catherine, died in 1807.

I wonder if someone knows more about these four siblings, why they lived in Denmark, didn't marry etc. and can give me hints to literature about them?